In summary, this invention relates to a new kind of thermoelectric circuit based on the Peltier and Seebeck Effects. It departs from what is conventional by applying a combination of novel principles, one of which amounts to a scientific breakthrough, being a discovery emerging from extensive diagnostic tests on a research prototype which was described in the specification of U.K. Patent Application No. 8,828,307 filed on Dec. 5, 1988, the latter also being based on U.K. Patent application No. 8,826,952 filed on Nov. 18, 1988.
The invention there disclosed aimed to obstruct heat flow between the hot and cold thermocouple junctions, whilst admitting the passage of electric current through the junctions in a way which involves a net energy conversion. A capacitative structure in which the dielectric served also as the heat insulator featured in that invention. In contrast, the invention to be described in this specification, does not obstruct heat flow but rather directs the heat flow along a junction interface to give it repeated opportunity to be involved in the thermoelectric power conversion before it reaches a position midway between the hot and cold external surfaces. This enhances the efficiency of power conversion, but, in itself, given a junction combination with a low thermoelectric power or a poor electrically conductive property, this is a technological feature offering only limited commercial advantage. It becomes particularly advantageous when combined with a novel method for enhancing the thermoelectric power as measured by the Seebeck coefficient of the thermocouple.
Since what is to be specifically described is a very compact thermopile system in which numerous junctions share in enhancing the voltage rating of the device, it is appropriate to refer to a prior proposal which forms the subject of U.S. Pat. No. 4,276,441. This patent names as inventor Kenneth T. Wilson and discloses a method of fabrication of a thermoelectric circuit using a multiplicity of thermocouples formed by metallic ink printing on a narrow strip substrate layer. The bimetallic junctions are formed by a melting operation and the disclosure in that patent specification is wholly concerned with assembly and production methods. There is no suggestion that any novel electrical operating principles are involved or that dimensional features are scaled to exploit those principles. Therefore, the device fabricated according to the Wilson patent, though providing for simple voltage enhancement by series connection of a multiplicity of thermocouple junctions, suffers from the poor efficiency characteristic of conventional base metal thermopiles. It must have substantial heat losses owing to thermal conduction through the metal conductor sections linking the junctions.
Other than the description in their own as yet unpublished U.K. Patent Applications Nos. 8.826,952 and 8,828,307 mentioned above, the inventors also declare that they have no knowledge of any prior disclosure which is based on the conception that a thermocouple device can operate by current passage in a fast-cycling A.C. mode. This principle features in the invention to be described. Indeed, the normal expectation of such a proposal would be that the cyclic heating and cooling of each thermocouple junction at the operating frequency should have no advantage for energy transfer and should merely generate ohmic loss and lose heat by thermal conduction.